ESA, tax credits and childcare costs

Hi everyone, looking for some help with the above.

Briefly....Oh and I have a 4 year old who goes to a childminder while we work. Oh was self employed but became ill and had to go onto contribution based employment and support allowance. Obviously as he is ill he is unable to look our LO who continues to go to childminders. Previously we received extra tax credits to cover some of the childcare costs.
When OH became ill he informed tax credit people but heard nothing back from them. Now we have had a renewal pack and have sent them final details of our earnings.
They say we are not entitled to child care element anymore and haven't been since OH became sick. They say we have been overpaid by £1500.
I only earn £700 a month and CM fees are £460. OH is too ill to look after him and he gets £70 ESA. He has been receiving ESA for about 20 weeks.

I am totally baffled how can my oh look after our LO if he is too ill too work.

Does this sound right to anyone or do you think there is a mistake somewhere?
I have looked on the tax credit website but am no wiser.

Would really appreciate any help, thanks